What does the prefix "hyper-" mean versus "hypo-" in medical terms?

Hyper means above, excessive, or more than normal, while hypo means below, deficient, or less than normal. These are among the most important prefixes because they appear in hundreds of medical terms. Hyperglycemia means high blood sugar, while hypoglycemia means low blood sugar. Hypertension means high blood pressure, while hypotension means low blood pressure. Hyperthyroidism means an overactive thyroid, while hypothyroidism means an underactive thyroid.